Thus linux-p4-64 and pi4-64-bootloader.
linux-p4-64 is the foundations linux sources compiled arm64 for the pi4.

pi4-64-bootloader is the other needed /boot files.
ie: fixup4*, start4*, cmdline.txt and a modified config.txt for arm64.
Also included are the brcmfmac43455 files.

So with these 2 deb's

linux-image-p4-64_5.4.40+-0_arm64.deb
pi4-64-bootloader_20200516-0_arm64.deb

You can debootstrap a sdcard with Devuan arm64 for the pi4.

So the tool to use is Devuan-pi4-os64

git clone https://github.com/ShorTie8/Devuan-pi4-os64
cd Devuan-pi4-os64
./Devuan-pi4-os64.sh

It grabs debootstrap_1.0.123+devuan1 and uses it.
You just need to supply a arm64 enviroment.

A arm64 version of the vcgencmd command is included too.
Along with dhcpcd5 ntp mlocate ssh wpasupplicant.
So you can go headless, if you want.
Login  root/rtyu

Have A Great Day
ShorTie